Five leg core for large transformers



1911.26, 1960 T, D GOR'DY 2,922,972

FIVE LEG CORE FOR LARGE TRANSFORMERS Filed Aug. 20, 1956 4 Shasta-Sheet [area/5r molqas 12 601-5731, fly fl w-26 1575 flf/brqgg.

Jan. 26, 1960 T. D. GORDY FIVE LEG CORE FOR LARGE TRANSFORMERS 4 Sheets-Sheet 3 Filed Aug. 20, 1956 7 m 17. 6 'fW/ Jan. 26, 1960 T GQRDY FIVE LEG CORE FOR LARGE TRANSFORMERS 4 Sheets-Sheet 4 Y Filed Aug. 20, 1956 fnvenlbr- Tbomas by 9 1.

H/lsfllforney United States Patent Ofiice 2,922,972 Patented Jan. 26, 1960 FIVE LEG CORE FOR LARGE 'IRANSFQRMERS Thomas D. Gordy, Pittsfield, Mass, assignor to General Electric Company, a corporation of New York Application August 20, 1956, Serial No. 605,185

'14 Claims. (Cl. 336-215) This invention relates to magnetic cores for stationary electrical induction apparatus and more particularly to threephase stacked lamination cores having five legs.

This application is a continuation-in-part of my application Serial No. 496,984, filed March 28, 1955, and assigned to the assignee of the present application.

his well known that a grain oriented magnetic material having a path of least magnetic reluctance parallel to the direction of grain orientation may be formed by rolling strips of magnetic material, the orientation extending in the direction of rolling. Such materials have been used to form transformer cores having greatly improved magnetic characteristics. A typical core employing such materials is disclosed in United States Letters Patent ;No. 2,467,823 which issued on April 19, 1949, on an application of T. D. Gordy and assigned to the present assignee.

It is also well known that many advantages may be derived in a stacked lamination transformer core by longitudinally splitting or dividing the yoke and leg sections. For example, such a design provides decreased core losses due to corner effects, the narrower laminations are more easily handled, circulation ducts may be readily provided, and stocking of non-standard width lamination material for fabricating the cores may be unnecessary. This type of core disclosed in United States Letters Patent No. 2,698,924 which issued January 7 4, 1955, on an application of T. D. Gordy and also assigned to the present assignee.

As the transmission voltages of electric power have increased and the power output of generating equipment has also increased, there has been a demand for larger and larger transformers to handle these steadily increasing loads. Railroad clearances have limited the height of power transformers to be shipped by rail, and thus in recent years efforts of transformer manufacturers have been increasingly directed toward increasing the capacity of power transformers without increasing their overall height. In the case of three phase power circuits it has been found that decreased height may be obtainedby using a five-leg transformer, with three central winding legs extending between a pair of yoke members and a pair of outer side legs also extending between the yoke members. Normally five-leg cores of the stacked laminationtype have about 57.7 percent of the main leg cross-sectional area in the yokes and the side legs. This reduction in yoke height provides a transformer having greater winding window height than a conventional three-leg transformer having the same overall height. Although this height reduction may seem negligible in comparison to the total height of large power transformers, the size limitations are very critical and small decreases such as this must be taken advantage of in order to increase the power capacity of transorm r "It'is an object of this invention to provide an improved.

five-leg transformer core for the three phase circuits employing grained oriented laminations of magnetic material and having longitudinally split windinglegs.

A further object of this invention is to provide an improved five-leg transformer core having mitered joint construction and longitudinally split winding legs and being constructed of grain oriented magnetic material.

Briefly stated, in accordance with one aspect of my invention 1 have improved the electrical characteristics of five-leg stacked lamination type transformer cores by providing mitered joint type of construction and employing grain oriented magnetic material. The transformer core losses are greatly reduced by longitudinally splitting the three winding legs. These improvements in five-leg cores are made possible by a unique arrangement of magnetic insert members for joining the winding legs and the yoke members in the core of my invention.

My invention will be more clearly understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings,

Fig. 1 is a perspective partially exploded view of a five-leg transformer core illustrating one embodiment of the core construction of my invention,

Fig. 2 is a front elevation of a Winding leg and yoke joint of the transformer core of Fig. 1,

Fig. 3 is a perspective partially exploded view of a modification of a winding leg and yoke joint of the transformer core of Fig. 1,

Fig. 4 is a front elevation of the joint arrangement of Fig. 3,

Fig. 5 is a perspective partially exploded view of another modification of a winding leg and yoke joint of the transformer'core of Fig. 1,

Fig. 6 is a front elevation of the joint of Fig. 5,

Fig. 7 is a perspective partially exploded view of still another modification of a winding leg and yoke joint of the transformer core of Fig. 1,

Fig. 8 is a front elevation of the joint of Fig. 7,

Fig. 9 is a front elevation of a modified form of fiveleg transformer having a reduced height in the ends of the yoke members,

Fig. 10 is a partially exploded view of one form of a Winding leg and yoke joint of the transformer core of Fig. 9,

Fig. 11 is a front elevation of the joint of Fig. 10,

Fig. 12 is a partially exploded view of another form of a winding leg and yoke joint of the transformer core of Fig. 9,

Fig. 13 is a front elevation of the joint of Fig. 12,

Fig. 14 is a perspective partially exploded view of still another form of a winding leg and yoke joint of the transformer of Fig. 9,

Fig. 15 is a front elevation of the joint of Fig. 14,

Fig. 16 is a perspective partially exploded View of another form of a winding leg and yoke joint of the center winding leg of the transformer of Fig. 1, and

Fig. 17 is a front elevation of the joint of Fig. 16.

Referring now to Fig. 1, a transformer core formed of flat stacked laminations of strips of magnetic material is therein illustrated comprised of a pair of outer leg members 10 and 11 and three central winding leg members 12, 13 and 14 extending in perpendicular relationship at spaced intervals between a top yoke member 15 and a bottom yoke member 16, and defining a pair of identical central rectangular core windows 17 and 18 and a pair of identical outer rectangular core windows 19 and 20. The outer core windows 19 and 20 have the same height as the central core windows 17 and 18.

As seen in Fig. 1, the central core leg members 12, 13, and 14 are longitudinally split normal to the plane of the lamination strips to form a pair of parallel leg 7 sections separated by a duct extending transverse to the tions of magnetic material.

Thelaminations of the leg'and yoke members are preferably formed of strips of grain oriented magnetic material, such as rolled silicon steel. in laminated form with the grain orientation extending parallel to the lengthwlse dimension of thestrips. j j I each layer of the core the respective -.leg section strips are joinedto the unsplit yoke laminations and also to inserts of grain oriented magnetic material. Thus, in the outermost layer .of the core of Fig. 1, leg section strip 25 of leg'section 22 joins its respective outer yoke member-strip 26 and one side of triangular insert 27, and leg section strip 2 8 ofleg' section 21 joins its respective outer yoke member strip 29 and a second side of insert 27. The yoke member strips 26 and 29 also join the insert 27. In this modification of T-joint the insert is isosceles triangular shaped and preferably joins 'the yoke and leg strips at substantially 45-angles to the length ofthe strips and the leg strips join the yoke strips along a joint that is 45 in respect to the length of the strips. The remaining side of the triangular insert is in linewith-the outside'edge of the yoke member strips. The grain orientation of the strips and insert isindicated by the arrows, the insert orientation being in a direction parallel to the right side of the insert.

In the second layer of laminations, leg section strip 30 of legsection 22joins yoke member strip 31 and'triangular msert 32, and leg section strip 33 of leg section 21 joins yoke member strip 34 andinsert 32. This T-' joint is identical to the T-joint of the outermost layer with the exception that the grain orientation of the insert 32 isparallel to the left side of insert and the insert 32 is slightly smaller than the insert 27; The joints of the remaining layers of the core alternate between the two previously described types so that joints of alternate strips overlap in the manner illustrated in Fig. 2.

The joints between the outer leg members 10 and 2t and the yoke members'lS and 16 are preferably of the mitered overlap type-as illustrated in Fig. 1.

.The cross-sectional area of the yoke and outer leg sections is preferably about 57.7 percent of the'cross-sectional area of each leg member. The reasons for this are well known and will not be presented herein. Variationsfrom this relationship may be used as will be shown later, but in some cases may result in increased harmonic or fundamental flux in certain parts of the core. Suppressor windings may be employed on the core in order to reduce flux distortion and thus improve the sound level of the transformer employing the core by reducing harmonic components. 1 a

The leg laminations of the core of Fig. 1 may be held together by means of bolts passing through the center leg ducts and tie plates adjacent the sides of the'legs. This methodof clamping provides uniform clamping pressure and decreases compression losseffects in the legs. Other conventional means may be employed to hold the yoke laminations together and clamp the leg members to the yoke members. we

In the modification ofT-joint illustrated in Figs. 1 and 2 the apexes of the triangular inserts extend into-the center of. the duct between the legsections; and alter nate inserts are of different sizes. A modification of this joint using triangular inserts is illustrated in Figs. 3 and 4. In this modification, the insert 40 of the outermost-layer and the insert-41 of the second layer are the same size, but are displaced in alternate core layers so that the apexes of alternate inserts join alternate leg sec tions. r

InFigs. and 6 is illustrated another modification of the T-joint between the leg sections and the yokemembers. In this modification. a" trapezoidal insert is employed, with the insert 45 of the outermost layer being identical to the insert 46of the second layer,the inserts of alternate layers being reversed. Here one base of the outermost trapezoidal insert 45 joins one leg section strip and its respective yoke member strip 26, the other base joins the other yoke section strip 29 in the T-joint, another side of the trapezoidal insert is in line with the outside edge of the yoke member strips, and the remaining side joins the other leg section strip 28 in the T-joint. Still another form of insert for the core of Fig. 1 is illustrated in Figs. 7 and 8. Here the insert 50 for the outermost layer. is pentagonal with one ,side butting against the leg section strips 25 and 28 along a line p n pendicular to the length of the leg strips, the next adjacent sides being perpendicular to'the first side and joining the leg strips 26' and 29 at right angles for a portion of their length, and the remaining sides joining the respective yoke strips at an angle of 45 to the length of the strips and forming an apex at the bottom of the yoke strips and equidistant from the outside edges of theleg strips 25 and 28. The second layer insert 51 is triangular in shape and has one side joining a portion of the leg section strips and 33 along a line perpendicular to the length of the leg strips and the remaining sldes joining the yoke strips 31 and 34 which also join each other. .This modification of T-joint has the advantage that the yoke members may be readily removed without removing the inserts 50 and 51.

Referring now to Fig. 9 therein is illustrated a modified form of five-leg core having three parallel central winding leg members 60,61, 62, a pair'of side leg members 63 and 64 disposed outwardly'of the winding leg members, and a bottom and top yoke member, 65 and 66 respectively, joining the ends of the leg members. In

7 this modification the winding legs'are longitudinally split as in the case of the 'core of Fig. '1, but the widths of the side leg members and yoke members have been varied in order to obtain optimum utilization of core materials. In other words, by reducing the width of the side leg members 63 and 64 and the end portions 67 of the yoke members'that extend beyond the winding leg members and join the side leg members, and by increasing the width of the central portions of the yoke members that extend between the winding leg members, the core will haveless weight than the core of Fig. 1 without any substantial change in magnetic characteristics.

I In this modification, the inserts 68 joining the center winding leg member 61 and the yoke membersmay be of the types previously described in reference to Fig. l Theinserts joining the outer winding leg members 60 and 62 and the yoke members must be somewhat diiferent, however, due to the reduced Width of the end portions 67 of the yoke. Typical means for joining the leg members 60 and 62 and the yoke members are illustrated, in Figs. 10, 11, 12, and 13.

1 In one such type of core joint, asillustrated in Figs. 10 and 11, an outer layer is comprised of a substantially rectangular shaped insert 70 joining the split leg -.sections 71 and 72, the reduced width yoke strip 73,

and the increased width yoke strip 74. In this joint, one side of the insert 70 and leg member strip 72 join the increased width yoke strip 74 at an angle of about 4 to the lengthwise direction of the strip 74, the outside edge of the yoke strip forming an acute angle with the line of the joint. The 'leg member strip 72 also joins an adjacent side of the insert 70[ The opposite side of the rectangular insert joins the leg member strip '71 and the yoke member strip 73, thereby leaving the remaining side of the insert unjoined and defining a sloping edgev between strip 74 and strip 73. Leg member strip '71 also joins yoke member strip 73. v

The next adjacent layer of core laminations is similar to the outside layer with the exception that the insert 75 is somewhat smaller than the insert 70 to provide an over-lapping joint, and the direction'ofgrain orientation is reversed. r a

In another type of joint (see Figs. 12 and 13) for the core of Fig. 9 the outside layer of strips is similar to that of the joint' illustrated in Figs. 10 and 11, with the insert 80 being similar to insert 70, but the insert 81 of the adjacent layer is offset to provide overlapping joints rather than being smaller. Thus the insert 80 and the insert 81 may be identical with the exception of the direction ofgrain orientation.

In still another type of joint (Figs. 14 and 15) for the core-of Fig. 9 the insert 90' is generally pentagonal, and has one edge 91 joining the strip yoke 74 at an angle of substantially 45 to the lengthwise direction of strip 74. Another edge 92 of the insert 90' joins the leg strip 72 at substantially a 45 angle to'the lengthwise direction of the strip 72, and similarly an edge 93 of the insert 90 joins the leg strip 71 at substantially a 45 angle to the lengthwise direction of the strip 71. The edge 94 of insert 90 defines an outside edge of the transformer core, and the edge 95 of the insert 90 joins the narrower yoke laminations 73 in a joint substantially perpendicular to the lengthwise direction of. the strip 73. As in the core joints of Figs. 913', the strip- 71 joins the strip 73 at an angle of substantially 45 to the lengthwise direction of these strips, and similarly the strip 72 joins the strip 74 at substantially a 45 angle to the lengthwise direction of these strips.

In the next adjacent lamination layer, the insert 96 has a similar shape to the insert 90, but may be somewhat smaller and laterally displaced to provide for overlap between the joints of adjacent layers. The insert 96 joins the respective strips of the yoke and leg members at angular relationships similar to' thatof the insert 90. The grain orientation of inserts of adjacent layers is at substantially right angles as shown by the arrows.

The modification of Figs. 14 and 15 is especially-desirable from the standpoint of fabrication of a core, since the end sheeting of the core (i.e., fitting of the yoke strips in place) is thereby facilitated. In the fabrication of the core the insert members are generally located in a position before the yoke members, and in the arrangement of Figs. 14 and 15, it may be seen that the yoke strips may be simply lowered into position, rather than fit in position as required in the structures of Figs. 10-12.

This is possible since the end of each portion of each yoke lamination at the joint extends at least as far in the lengthwise direction of the lamination strip as all other portions of the lamination toward the innermost of the strip, i.e., the edge of the strip adjacent the winding window.

Referring now to Figs. 16 and 17, wherein is illustrated another modification of a joint for the core of Fig. 1, the insert 100 of one layer of laminations is substantially square and is disposed so that each of the edges joins one of the strips 25, 26, 28 and 29, and so that the joints between the insert and the strips are all at substantially 45 angles to the lengthwise direction of the respective strips. The strips 25 and 28 join the yoke strips 26 and 29 respectively at substantially 45 angles to the lengthwise direction of these strips. The insert 100 is small enough so that it does not reach the outer edge of the core, and thus a joint 101 is provided between the yoke strips 26 and 29, the joint 101 being perpendicular to the lengthwise direction of the strips 26 and 29. The insert 102 of the adjacent layer of laminations has the same sizeand shape as the insert 100, andjoins its respective strips at the same angular relationships as the insert 100. The insert 102, however, is displaced a short distance along the lengthwise direction of the yoke strips to provide an overlap between thejoints of adjacent layers. The grain orientation of the inserts of adjacent lamination layers is at substantially right angles, as shown by the arrows in the drawing.

The joint arangement of Figs. 16 and 17 has the advantage, as previously disclosed in reference to the joint of Figs. 14 and 15, in the reduction of the difliculties of same size and shape, and also that the joints between the core strips and the inserts are at substantially 45 angles to the lengthwise direction; of the strips for improved magnetic characteristics.

From the preceding discussion it is seen that this invention provides an improved five-leg threephase transformer. The three winding legs of the transformer have longitudinal splits to improve magnetic characteristics, simplify fabrication, provide a convenient cooling duct, and also to eliminate the necessity for stocking of nonstandard wide lamination strips. This construction is made possible by aunique joint arrangement.

It will be understood, of course, that whilethe forms of the invention hereinshown and described constitute preferred embodiments of the invention, it is not intended herein to illustrate all of the possible equivalent forms What I claim as new and desire to secure by Letters Patent of the United Statesis:

l. A five-leg transformer core assembly formed of flat stacked laminations of magnetic material comprising a pair of outer leg members and three central winding leg members extending in perpendicular relationship at spaced intervals between a pair of yoke members and defining a pair of identical central rectangular core windows and a pair of identical outer rectangular core windows, said outer corewindows having the same height as said central core -windows,-said three winding leg members each being longitudinally divided normal to the plane of said laminations to form a pair of parallel leg sections 2. A five-leg transformer core assembly formed of flat stacked laminations of magnetic material comprising a pair of outer leg members and three central winding leg members extending-in perpendicular relationship at spaced intervals between a pair of yoke members and defining a pair of identical central rectangular core windows and a pair of identical outer rectangular core windows, said outer core windows having the same height as said central core windows, said three winding legs eachbeing longitudinally divided to form a pair of parallel leg sections separated by a duct extending transverse to the plane of said laminations, said magnetic material being grain oriented with said orientation extending substantially parallel to the lengthwise direction of said yoke and leg members.

3. A five-leg transformer core assembly formed of a plurality of flat-stacked strips of magnetic material having grain orientation substantially parallel to the lengthwise direction of said strips, said core assembly comprising a pair of parallel yoke members, a pair of outer leg members extending in perpendicular relation between the ends of said yoke members, three central winding leg members extending in perpendicular relationship between said yoke members at spaced apart intervals, said leg and yoke members defining a pair of identical central core windows and a pair of identical outer core windows having the same height as said central core windows, said three winding leg members each being longitudinally divided normal to the plane of the strips of said winding leg members to form a pair of parallel leg sections separated by a duct extending transverse to the plane of the strips of said winding leg members, and a grain oriented insert of magnetic material joining each pair of parallel coplanar leg section strips to respective yoke member strips.

4. The core assembly of claim 3 wherein the inserts are substantially square and the edges of said inserts join the strips of said yoke sections and winding leg members at angles of substantially;45 to the lengthwise directions of the strips of said yoke sections and winding leg membe s .r V

5. Thecore assembly of'clairn 3 wherein the joints between said inserts and said leg section strips and respective yoke member strips are staggered in alternate layers of said strips.

6. A five-leg transformer core assembly formed of a plurality of flat strips of magnetic material having grain orientations substantially parallel to the lengthwise direc tion of said strips, said core assembly comprising a pair of parallel yoke members, a pair of outer leg members extending in perpendicular relationship between the ends of said yoke members, three central winding leg members extending in perpendicular relationship between said yoke members at spaced apart intervals, said legand yoke members defining a pair of identical central core'windows and a pair of identical outer core windows having the same height assaid central core windows, said three winding leg members :each' being longitudinally divided normal to the plane of said winding leg members to form a pair of parallel leg sections separated'by a duct extending transverse to the plane of the strips of said winding leg members, and a substantially square grain oriented insert of magnetic material, joining each 'pair'of parallel coplanar leg section strips to respective yoke member strips, said inserts being arranged to that the joints be- .tween the edges of said inserts and the yoke and winding member strips are at substantially 45 to the lengthwise direction of said yoke and winding leg member strips, the

end of each portion of the yoke member strips extending at least as far as the lengthwise direction of said. yoke member strips as all other portions of said yoke member strips toward the window of said core assembly.

7. A five-leg transformer core assembly formed of a plurality of flat-stacked strips of magnetic material having grain orientation substantially parallel to thelengthwise direction of said strips, said corejassembly comprising a pair of parallel yoke members, a pair of outer leg the plane of said strips to form a pair of parallel leg sections separated by a duct extending transverse to the plane of said strips, said T-jointfbeing comprised of a' grain oriented msert of magnetic material comprised of a grain oriented insert of magnetic material joining each' pair of parallel coplanar leg section stripsand their respective yoke member strips, the joints between said inserts andsaid leg section strips and said respective yoke member strips beingstaggered in alternate layers of said strips, and the insert members for adjacent layers of said strips having their respective grain orientations disposed in such a manner as to present favorable grain orienta tions for at least two different directions of magnetic flux I travel throughsaid insert members.

8. The core assembly of "claim 7 wherein said inserts are in the shape of isoceles triangles with one side being in 'line with theoutsidefedge of the yoke member strips and the remaining sides each joining one leg section strip and a respective yoke member strip,

.40 members extending in perpendicular'relation between the 9. The core assembly of claim 7 whereinjsaidinserts are trapezoidal shaped having one'base joining one leg? section strip and its respective yoke member strip, the

other base joining the other yoke section strip in said T-joint, one side being in line withithe outside edge of said yoke member strips, and the remaining side joining" the other leg section strip in said T-joint.

10. The core assembly of claim 7 wherein the outer leg members and first portions-of the yoke membersextending between the outer leg members and the Winding leg members are narrower than second yoke member portions extending between the winding'leg members; a

and said inserts arej'substantially rectangular shaped having one side joining'said second yoke portion along a joint that forms an acute angle with the outsideedge of said second yoke member portion, van adjacent sideof said insert joins one leg member strip, the opposite side of said insert joins another leg member strip and a first yoke member portion strip, .and the'remaining side of said insert defines a' slope betweensaid first portion-strip and said second portion strip.

11. The core'assembly of claim 7' wherein the end of g each portion of each yokelamination strip at said joint extends at least as far in the lengthwise direction of the said yoke member strips as all other portions of said end portion of the joints of said yoke member strip toward the window of said core.

12. The core assembly of claim 11 whereinsaid in serts are substantially square and their sides join the winding leg member. and yoke member strips at substantially 45 angles to the lengthwise direction-of said winding leg member and yoke member strips.

, 13. The core assembly of claim 11 wherein the inserts of one of said layers is pentagonal and has one side joining a pair of leg. section strips normal to their lengthwise direction and the remaining adjacent pairs of sides each-joining one of said yoke member strips, and the insert of an adjacent layer is triangular and has one side joining a pair of leg section strips normal to their length-, wise direction.

.1'4. Thecore assembly of claim 11 wherein the outer leg members and first portions of the yoke membersextending between the outer leg members and winding leg members are narrower than second yoke member portions extending between the winding leg, members, and said inserts are substantially pentagonalshaped having a first side joining said second yoke portion along the joints that form a substantially 45 angle With the lengthwise direction of said second yoke member portion, second and third sides joining leg member strips at substantially 45 angles to the lengthwise direction of said leg member strips, a fourth side joining said first portion along a joint substantially perpendicular to the lengthwise direction of said first yoke portion, and a fifth side defining a slope between said first portion strip and second portion Great Britain l Sept. 6, 1950 ans 

